Understanding Gas Fees

What Are Gas Fees?

Gas fees are the transaction fees you pay to the blockchain network to process your transaction. They go to the validators (or miners) who maintain the network — not to Swaptain or any intermediary.

Every blockchain transaction — sending tokens, swapping, approving a token contract — requires gas.

Why "Gas"?

The term comes from Ethereum. Just like a car needs gasoline to run, a transaction needs "gas" to execute on the blockchain. The more complex the transaction, the more gas it requires.

How Gas Fees Work on Different Chains

UTXO Chains (Bitcoin, Litecoin, etc.)

Fees are based on transaction size (in bytes), not value:

A transaction sending 0.001 BTC costs the same in fees as one sending 100 BTC
Fees increase when the network is congested (more people competing for block space)
Bitcoin fees can range from a few cents to over $10 during peak congestion

EVM Chains (Ethereum, BNB Chain, Avalanche, etc.)

Fees are calculated as: Gas Used × Gas Price

Gas Used — depends on transaction complexity (a simple transfer uses ~21,000 gas; a swap might use 100,000+)
Gas Price — set by network demand (measured in "gwei" on Ethereum)

This is why Ethereum gas fees are famously variable — during high demand, the gas price spikes.

Cosmos Chains

Fees are generally low and predictable. Cosmos chains use a simpler fee model with minimal variation.

Gas Fee Comparison

| Chain | Typical Transfer Fee | Typical Swap Fee | Variability | |-------|---------------------|-----------------|-------------| | Bitcoin | $0.50 - $5.00 | N/A (UTXO) | Moderate | | Ethereum | $0.50 - $20.00+ | $2.00 - $50.00+ | High | | BNB Chain | $0.05 - $0.20 | $0.10 - $0.50 | Low | | Avalanche | $0.01 - $0.10 | $0.05 - $0.30 | Low | | Polygon | $0.001 - $0.01 | $0.01 - $0.05 | Low | | Arbitrum | $0.01 - $0.50 | $0.05 - $1.00 | Moderate | | Base | $0.001 - $0.10 | $0.01 - $0.50 | Low-Moderate | | Cosmos | $0.01 - $0.05 | $0.01 - $0.10 | Low |

These are approximate ranges and can change based on network conditions. Layer 2 chains (Arbitrum, Base, Optimism) are generally much cheaper than Ethereum mainnet.

Why Do Gas Fees Spike?

Gas fees increase when more people are trying to use the blockchain than it can handle:

Market volatility — sudden price movements cause a rush of trades
NFT mints — popular NFT launches flood Ethereum with transactions
Token launches — new token listings cause trading frenzy
Network events — airdrops, governance votes, protocol upgrades

How Gas Fees Affect Your Swaps

When you swap on Swaptain, gas fees apply on both chains involved:

Source chain gas — to send your tokens to the THORChain vault
Destination chain gas — for THORChain to send you the output tokens

Both fees are included in the quote Swaptain shows you. The output amount already accounts for gas costs.

On EVM chains, you need the native token (ETH, BNB, AVAX, etc.) in your wallet to pay gas fees — even if you're swapping an ERC-20 token. If you only have USDC in your Ethereum wallet and no ETH, you can't initiate a swap.

Tips for Minimising Gas Costs

Use Layer 2 chains — Arbitrum, Base, Optimism, and Polygon have much lower fees than Ethereum mainnet
Avoid peak hours — Ethereum gas tends to be lower on weekends and during off-peak hours (late night/early morning UTC)
Batch actions — if you need to make multiple swaps, consider doing them in fewer, larger transactions
Choose BNB Chain or Avalanche — for routine swaps, these chains offer consistently low fees

If gas fees on Ethereum are too high for your trade size, consider whether the same token is available on a cheaper chain. Many popular tokens (USDC, USDT, etc.) exist on multiple chains with the same value but much lower fees.

Token Approvals (EVM Only)

On EVM chains, before you can swap an ERC-20/BEP-20 token for the first time, the token contract must be "approved" for spending. This approval is a separate transaction that costs gas.

With Swaptain's Auto Approve setting enabled (the default), this happens automatically as part of the swap flow. The gas cost for approval is typically small compared to the swap itself.